On 01/01/2011 08:09 PM, Artem Belevich wrote:
On Sat, Jan 1, 2011 at 10:18 AM, Attila Nagy<b...@fsn.hu> wrote:
What I see:
- increased CPU load
- decreased L2 ARC hit rate, decreased SSD (ad[46]), therefore increased
hard disk load (IOPS graph)
...
Any ideas on what could cause these? I haven't upgraded the pool version and
nothing was changed in the pool or in the file system.
The fact that L2 ARC is full does not mean that it contains the right
data. Initial L2ARC warm up happens at a much higher rate than the
rate L2ARC is updated after it's been filled initially. Even
accelerated warm-up took almost a day in your case. In order for L2ARC
to warm up properly you may have to wait quite a bit longer. My guess
is that it should slowly improve over the next few days as data goes
through L2ARC and those bits that are hit more often take residence
there. The larger your data set, the longer it will take for L2ARC to
catch the right data.
Do you have similar graphs from pre-patch system just after reboot? I
suspect that it may show similarly abysmal L2ARC hit rates initially,
too.
I've finally found the time to read the v28 patch and figured out the
problem: vfs.zfs.l2arc_noprefetch was changed to 1, so it doesn't use
the prefetched data on the L2ARC devices.
This is a major hit in my case. Enabling this again restored the
previous hit rates and lowered the load on the hard disks significantly.
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